1. Technical Field
The present invention relates in general to processing sliders for hard disk drives and, in particular, to an improved system, method and apparatus for lapping hard disk drive sliders with soluble abrasives.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, the magnetic storage device or hard disk drive (HDD) includes one or more disks and a disk controller to manage local operations concerning the disks. The disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The read/write head comprises an electromagnetic coil writer, a reader, and a slider body. It flies over the magnetic disk to perform the read and write functions. To achieve optimum performance, the spacing between the transducer and the disk, called the magnetic space must be consistently maintained. The magnetic space has become consistently smaller over time with the increasing of recording areal density. The magnetic space is defined as the fly height plus the pole tip recession (PTR).
The PTR has been a major contributor to the magnetic space loss for high areal density products. The PTR is the height difference between the pole tips and a plane fitted to the ABS. It is caused by the differences in the removal rates of metal poles, alumina, and AlTiC in the slider abrasive finishing process. The slider abrasive finishing process critically affects the magnetic, electrical, and mechanical performances, as well as the stability of the recording heads. Therefore, ultraprecision abrasive finishing is a key technology in the final finishing of thin film magnetic recording heads.
Lapping is a material removal process for the production of flat surfaces by free-abrasive three-body abrasion. A loose abrasive and a hard lapping plate are used for this purpose. During lapping, besides three-body abrasive abrasion (i.e., rolling), some abrasives also temporarily embed in the lapping plate to cause some temporal two-body abrasion. High material removal rate can be achieved by free-abrasive lapping.
Nanogrinding is a fixed abrasive two-body abrasion process that uses fixed-abrasive embedded in a soft supporting body as a finishing process for producing flat and good surface finish. The material removal rate from fixed-abrasive nanogrinding is lower than from free-abrasive lapping, but it can produce superior surface planarity (e.g., less recession). The recording heads/sliders are finished by free-abrasive lapping followed by fixed-abrasive nanogrinding. High material removal is achieved by free-abrasive lapping, and good surface finish and planarity are obtained by fixed-abrasive nanogrinding. Appropriate chemical-mechanical interactions in fixed-abrasive nanogrinding (i.e., chemical-mechanical nanogrinding) result in further improvements in achieving good surface finish and planarization.
The planarity and surface finish from fixed-abrasive nanogrinding are superior to those from free-abrasive lapping. For example, with a rough lapping plate, the PTR can be improved to about 8 nm by fixed-abrasive nanogrinding process versus about 32 nm by free-abrasive process. With a fine lapping plate with a fixed-abrasive nanogrinding process, PTR can be improved to a mean of about 1.0 nm. In addition, fixed-abrasive nanogrinding is virtually scratch-free in contrast to the significant scratching of free-abrasive lapping.
Further planarity and surface finish improvements are achieved by adjusting mechanical and chemical interaction in fixed-abrasive nanogrinding and chemical-mechanical nanogrinding. Process integration and throughput issues are considered for free-abrasive and fixed-abrasive processes. Free-abrasive lapping process is recommended for high material removal rates (MRR), followed by the fixed-abrasive nanogrinding process for achieving excellent finish.
In the field of lapping and chemical-mechanical polishing (CMP), one major issue related to lapping soft metals such as gold, tin, antimony, etc., is the unintentional impregnation of the hard, insoluble abrasive particles into the soft and ductile metal. This contamination can affect the electrical or mechanical properties of the metal since the embedded abrasives can form electrical interconnections. One way to lap or CMP such metals is to use special CMP pads with water. However this occurs at much lower lap rates where the major mechanism of material removal is dominated more by polishing and etching rather than actual bulk material removal. Although these processes are workable, an improved solution that overcomes the limitations and problems associated with the prior art would be desirable.